四川自贡大山铺孙氏鳄属(Sunosuchus)一新种

A NEW SPECIES OF SUNOSUCHUS FROM ZIGONG, SICHUAN, CHINA

记述了在四川自贡大山铺发现的孙氏鳄一新种———蜀南孙氏鳄 (Sunosuchusshunanensissp .nov .)。新种窄长的吻部 ,小的颅顶平台 ,额骨沿中线具一纵嵴 ,一对裂隙状的前腭孔位于眶下孔之前方 ,方骨腹面的嵴B特别发育等 ,与孙氏鳄的其他种很相似 ,但新种的吻部特别窄长 ,为吻后部长度的 3倍 ,上颌凹特别发育 ,颅顶平台短而宽 ,颞间部宽度大于眶间部宽度 ,泪骨在眼眶前缘处隆起成嵴 ,下颞孔小 ,呈裂隙状 ,鳞骨侧缘不增厚 ,也无附着上耳盖的沟嵴状构造 ,基枕骨侧缘和外枕骨内腹缘具一明显的隆嵴等 。

A new mesoeucrocodylian, Sunosuchus shunanensis sp. nov., was described in t his paper. Its specimen was collected from the Lower Shaximiao Formation in the famo us Dashanpu Dinosaur Quarry, Zigong, Sichuan, China in 1983. This new species re sembles the others of Sunosuchus in having a narrow snout, a small cranial t able , a ridge along the midline of the frontal, a pair of anterior palatal fenestrae located well anterior to the suborbital fenestrae, and a strongly developed cre st B on the ventral surface of the quadrate. However, it can be distinguished fr om all other species of Sunosuchus on the basis of the following characters: a r elatively narrow and elongate snout that attains a length 3 times that of the po storbital region, a pair of well developed maxillary depressions that occupy the posterior half of the maxilla, a relatively short but wide cranial table that a ttains a length-width ratio of 0.65, the interfenestral region wider than the i n terorbital region, the lacrimal with a flange along the anterior border of the o rbit, a pair of small, split-shaped infratemporal fenestrae, the squamosal lack i ng the thickened or grooved lateral side, a flange along the lateral margin of t he basioccipital and medioventral margin of the exoccipital. In addition, this s pecies differs from S. junggarensis in lacking a ridge-like structure and d epres sion or fossa on the dorsal surface of the distal portion of the quadrate body, having a deep step between the main body of the pterygoid and its palatal proces s, and the palatine with a narrow anterior part and a broad posterior part. It d iffers from S. miaoi in that the frontal enters the supratemporal fenestra. It d iffers from S. junggarensis and S. shartegensis in lacking two or three rows of enlarged pits on the posterior dorsal surface of the frontal.